1. Field of the Invention
The present invention relates to a process for producing a hydrogenated aromatic polycarboxylic acid in which an aromatic ring of an aromatic polycarboxylic acid is hydrogenated and a process for producing a hydrogenated aromatic polycarboxylic anhydride. More specifically, the present invention relates to processes for industrially advantageously producing a hydrogenated aromatic polycarboxylic acid and an acid anhydride thereof each having a high purity at a good yield respectively, which are used as a raw material for functional polyimides having properties such as transparency and solvent solubility and a curing agent for functional epoxy resins having transparency.
2. Description of the Related Arts
A process in which an aromatic polycarboxylic acid, an alkaline metal acid thereof or an ester derivative thereof is nucleus-hydrogenated is known as a process for producing a hydrogenated aromatic polycarboxylic acid.
Available are, for example, a process in which pyromellitic acid or tetraethyl pyromellitate is hydrogenated on the conditions of a hydrogen pressure of 200 atm, a temperature of 150° C. and a reaction time of 3 days using a Raney nickel catalyst (Journal of Organic Chemistry, vol. 28, p. 1770 (1963)) and a process in which a pyromellitic acid aqueous solution is hydrogenated on the conditions of a hydrogen pressure of 2.7 atm, a temperature of 60° C. and a reaction time of 1.5 hours in the presence of a rhodium catalyst (Journal of Organic Chemistry, vol. 31, p. 3438 (1966)). Also, known is a process in which pyromellitic dianhydride is esterified with 1-propanol and in which an ester derivative thereof is hydrogenated at a hydrogen pressure of 100 kg/cm2 G and a temperature of 130° C. for 2.5 hours in the presence of a ruthenium catalyst (Japanese Patent Application Laid-Open No. 325196/1996 and Japanese Patent Application Laid-Open No. 325201/1996). Further, known as well is a process in which trimellitic acid is dissolved in a mixed solvent of tetrahydrofuran and water and hydrogenated at a hydrogen pressure of 1400 psig and a temperature of 60° C. for 4 hours in the presence of a 5 weight % rhodium catalyst carried on carbon having a surface area of 940 m2/g or more (U.S. Pat. No. 5,412,108).
In the fields of functional polyimide and a functional epoxy resin curing agent in which a hydrogenated aromatic polycarboxylic acid is used as a raw material, raw materials having less impurities are desired. It is difficult to separate an unreacted aromatic polycarboxylic acid from a hydrogenated aromatic polycarboxylic acid by crystallization, and therefore the conversion rate in hydrogenation reaction has to be elevated to 99.8% or more in order to obtain a hydrogenated aromatic polycarboxylic acid having a high purity. Further, it is required to reduce the contents of alkali metals, halogens and ashes.
However, in the process described in, for example, Journal of Organic Chemistry, vol. 28, p. 1770 (1963) described above, unavoidable is contamination caused by inorganic matters such as alkali metal originating in alkali used when dissolving the raw materials and chlorine originating in an acid used when recovering 1,2,4,5-cyclohexanetetracarboxylic acid from the reaction liquid.
Also, in the process described in Journal of Organic Chemistry, vol. 31, p. 3438 (1966) described above, the conversion rate and the selectivity in hydrogenation reaction are not satisfactory, and unreacted pyromellitic acid remains. It is difficult to separate unreacted pyromellitic acid from nucleus-hydrogenated 1,2,4,5-cyclohexanetetracarboxylic acid by crystallization, and therefore the conversion rate in hydrogenation reaction has to be elevated to 99.8% or more in order to obtain 1,2,4,5-cyclohexane-tetracarboxylic acid having a high purity.
Further, in the process via an ester derivative disclosed in Japanese Patent Application Laid-Open No. 325196/1996 and Japanese Patent Application Laid-Open No. 325201/1996, the reaction step is long, and the reaction apparatus is complicated, so that the above process is not necessarily advantageous in terms of a production cost.
In addition thereto, metals such as iron, chromium, nickel and molybdenum eluted from a reaction apparatus are considered to be impurities, but they can be avoided by making the reaction apparatus out of a material having a strong acid resistance.
On the other hand, when a catalyst was repeatedly used in nucleus-hydrogenating an aromatic polycarboxylic acid to produce a hydrogenated aromatic polycarboxylic acid, observed was the phenomenon that an activity of the catalyst was reduced in several frequencies and that the conversion rate in hydrogenation reaction was deteriorated to a large extent. In respect to the activation of a catalyst used for hydrogenation reaction, it is described in U.S. Pat. No. 5,412,108 that impurities can be removed by washing the catalyst with polar solvents such as ethers, esters, aliphatic carboxylic acids and ketones and aromatic compounds such as benzene, toluene, xylene to make it possible to repeatedly use the catalyst. However, washing the catalyst with a solvent which is different from the reaction solvent is not necessarily advantageous as an industrial process. Further, it is described in Japanese Patent Application Laid-Open No. 159059/1989 that a ruthenium hydrogenation catalyst which is used for partial nucleus-hydrogenation reaction of an aromatic compound and reduced in an activity can be reproduced by bringing it into contact with oxygen in a liquid phase, for example, in a state in which a catalyst is dispersed in a suitable liquid or a state in which the catalyst is impregnated with the liquid, that is, in a state in which at least the surface of the catalyst is covered with the liquid.
On the other hand, it is known that an acid anhydride is obtained by subjecting an aromatic polycarboxylic acid to dehydration reaction. For example, 1,2,4,5-cyclohexanetetracarboxylic dianhydride is produced by subjecting 1,2,4,5-cyclohexanetetracarboxylic acid to cyclodehydration.
In general, a method carrying out heat treatment or a method using a dehydrating agent is used for dehydrating and ring-closing carboxyl groups which are adjacent and bonded to an aromatic or non-aromatic (alicyclic) six-membered ring to synthesize a cyclic acid anhydride. Known as well is a method in which refluxing by heating is carried out in the coexistence of an acid anhydride such as acetic anhydride and propionic anhydride as the dehydrating agent. In this case, hydrocarbons, halogenated hydrocarbons, esters, ketones, ethers and aliphatic acids each having a boiling point of 50° C. or higher may be added as a solvent.
A method in which refluxing by heating is carried out using acetic anhydride is known as a method for subjecting 1,2,4,5-cyclohexane-tetracarboxylic acid to cyclodehydration (refer to Japanese Patent Publication No. 23339/1995 and Japanese Patent Application Laid-Open No. 325196/1996).
In the field of functional polyimides in which a hydrogenated aromatic polycarboxylic acid anhydride is used as a raw material, the raw materials which are reduced in impurities and have a high purity are desired.
However, mere heat treatment of, for example, 1,2,4,5-cyclohexanetetracarboxylic acid results in coloring of the crystals. Further, as described in Japanese Patent Application Laid-Open No. 325196/1996, if 1,2,4,5-cyclohexanetetracarboxylic acid is subjected to cyclodehydration using acetic anhydride of a 10 times amount (weight ratio) based on 1,2,4,5-cyclohexanetetracarboxylic acid, dehydration reaction goes on without causing any problems, but because of a high solubility of 1,2,4,5-cyclohexane-tetracarboxylic dianhydride which is the intended product in acetic anhydride, the crystals of the above anhydride can not easily be recovered.
In order to solve this, it is considered to elevate the recovering rate of 1,2,4,5-cyclohexane-tetracarboxylic dianhydride crystals by a method such as condensing a reaction solution and condensing a mother liquid after separating the crystals, but it is disadvantageous as an industrial production process in terms of that the number of the equipments is increased and that the process is lengthened, and the crystals of 1,2,4,5-cyclohexanetetracarboxylic dianhydride are colored or impurities are introduced into the crystals of the acid anhydride to cause a reduction in the crystal purity.
Thus, it has been difficult in conventional techniques to obtain industrially advantageously a hydrogenated aromatic polycarboxylic anhydride.